JPS5886870A - Current detecting circuit - Google Patents

Abstract

PURPOSE:To detect the current flowing through a transistor of a current-feedback transistor driver at a low cost and with a small power consumption, by a method wherein a resistor is series-connected to a circuit connected to the base terminal of the transistor, and a current is drawn out from both ends of the resistor. CONSTITUTION:A resistor R2 is connected to the base circuit of a transistor Q2, and the current flowing through the transistor Q2 is detected from the base current of the transistor Q2 proportional to the emitter current of the transistor Q2. The base current of the transistor Q2 is determined according to the emitter current of the transistor Q2 and the turn ratio between windings T3a and T3b of a transformer T3. Since the turn ratio T3a/T3b is selected to be (hFE+1) times as much as the emitter current, the base current is 1/(hFE+1) of the emitter current.

Description

Detailed Description of the Invention (υ Technical Field of the Invention)Regarding a misfire 911it current detection circuit, in more detail, it is a current feedback type circuit that controls the on/off state of a butterfly-driven transistor according to the current flowing through the transistor. This relates to a circuit that detects the current flowing through the transistor in a transistor driving device.

(2) Problems with the conventional technology For example, in a DC-DC copy transistor, in order to protect against overcurrent R flowing through a transistor 7Kl, the current Rt flowing through the transistor is detected and the on/off time of the transistor is controlled by the detected current. However, when the current R flows too much, the on-time is shortened to perform DC-DC conversion.
As shown in FIG.

Qt is expanded according to the IEI diagram) transistor, L1 is the load.

TI is a transformer, E is a power supply, and R1 is a current detection resistor, which is proportional to the current detected by resistor R8 and is applied to the next voltage line control jump l, and the output of this control circuit 1 is connected to the transformer T.
,' controls the on/off time tw of the transistor Q through the circuit shown in Fig. 1.The electric current at flowing through the transistor Q is detected by the direct resistor gRs, which consumes a lot of power. Fig. 2 In the circuit of FIG.
This is a circuit for detecting the two constant electric current RYt [gu in Figure 1].
Although it is superior in terms of lower power consumption than the transformer T
! It is expensive because it uses wo.

(3) Purpose of the Invention In view of the above drawbacks, it is an object of the invention to provide a current detection circuit that is inexpensive and consumes little power and detects the current rlIlt flowing through the transistor of a current feedback transistor drive device. 4) Structure and object of the invention According to the present invention, the current flowing through the transistor is detected in a current feedback type transistor driving arrangement that controls the on-time or off-time of the transistor by the current flowing through the driven transistor. a circuit K connected to the pace terminal of said transistor;

A resistor is inserted in series, and the electrostatic current gt is extracted from both ends of the resistor in proportion to the emitter current flowing through the transistor. This is achieved by providing a first-class detection circuit with a high level of precision.

(5) Fruit of invention tIIAf1 Hereinafter, detailed examples of the non-invention will be described with reference to seven drawings.

Figure ga is a block diagram when the present invention is applied to a DC-DC converter, and in the figure, N: is a power supply, Ql is a transistor, Ts is a transformer, and R
9 is a current detection resistor, 2 is a control circuit, and 3 is a regulator I5! circuit,
4 Butterfly comparison circuit ref is a reference power supply, 5 is a pulse width modulator IT, T4 is a load quality generator, 6H is a rectifier and smoothing circuit, 7 is a detector, and 8 is a load t.

As shown in FIG. 3, the feature of the present invention is that a resistor R8t is connected to the base circuit of the transistor Ch, and the base current of the transistor Q is proportional to the electric current of the transistor Q. In the circuit of Figure 3, the base current of the transistor Ch is equal to the emitter current of the transistor Qt and the transformed lid.
's O'lil 7's a door' m b tv
Since the turns ratio THa/THb is selected to be (A, . . . +1) times the emitter current, the base current becomes 1/(A, I: +1) of the emitter current. 1 Voltage after detection [Assuming a constant value, the power consumption of the conventional circuit is Vl, (where Ayx is the current amplification factor when the emitter of transistor Q1 is grounded, and the voltage across the V expansion resistor.

r, tit resistance! − flowing collector current) but 9
In the circuit of FIG. 3 according to the present invention, power consumption is increased.

(Base voltage of IB transistor Q!, emitter current of 2 transistors Ch) Since the value of FK and FI is generally 10 or more, it is common to use conventional resistors for power consumption. Approximately 1 of the round trip in Figure 17
It becomes 1/0.

FIG. 4 shows another embodiment of the present invention. FIG. 4 shows the winding 11 connected to the collector of the winding Tsbk connected to the emitter of the transistor Q in the circuit of FIG.
11Tme, its turns ratio T@a/T, 61
In the case where kh and E are selected, the power consumption can also be reduced in this case.

(6) Effects of the Invention As explained in detail above, according to the present invention, the number of parts is the same as the conventional one, the power consumption is about one-tenth of the conventional one, and the current detection circuit is inexpensive because it does not use a transformer. can be obtained, so the effect is particularly great when applied to DC-DC co/parters and the like.

[Brief explanation of drawings]

1 and 2 are block diagrams of a conventional current detection circuit, FIG. 3 is a block diagram of an embodiment of a current detection circuit according to the present invention, and FIG. 4 is a block diagram of a circuit according to the present invention. FIG. 3 is a block diagram showing another embodiment. Qt butterfly in the diagram? "Fun Sister TsF! Transformer. R and each indicate the resistance for current detection. f4S1, 2nd page, WS3, 4th diagram

Claims (1)

[Claims] Driven transistors! A circuit for detecting the current Rt flowing through the transistor in a current feedback type transistor drive device which controls the on-time or off-time of the transistor by KR, and is connected to the base terminal of the transistor. A resistor is inserted in series into the circuit, and the resistor OW111 is proportional to the current RC flowing through the transistor. A current detection circuit whose purpose is to remove mold.